Why does the risk for cancer rise as we get older?
One reason may be a process that changes genes in ways that make it easier for cells to go from healthy to cancerous, according to research from the National Institutes of Health (NIH).
The process is called DNA methylation.
“Think of methylation as dust settling on an unused switch, which then prevents the cell from turning on certain genes,” said researcher Jack Taylor, MD, PhD. “If a cell can no longer turn on critical developmental programs, it might be easier for it to become a cancer cell.”
Methylation creates methyl groups (the dust of the metaphor above) that can attach themselves to DNA. If this occurs near the start of a gene, Dr. Taylor said, the gene can be switched off or silenced.
“This gene silencing is not necessarily bad or good,” he said. It depends on the context in which it occurs.
For example, some genes perform specific actions in cells. If methyl groups switch off these genes, those actions never occur. That’s bad if an action may have helped prevent cancer.
The researchers compared cancerous tissue with normal tissue, and they found increased methylation in cancer cells. They also found that DNA methylation is part of the normal aging process.
The human body adds about one methylation site (cells that contain methyl groups) per year, according to Zongli Xu, PhD, a colleague to Dr. Taylor and coauthor of the study.
“On your 50th birthday, you would have 50 of these sites that have acquired methyl groups in each cell,” Dr. Xu said. “The longer you live, the more methylation you will have.”
More methylation sites may mean a higher risk of cancer, the researchers suggested.
“If true, this process may explain some of the dramatic increases in cancer incidence as people age,” said Dr. Taylor.
Their findings appeared online in the journal Carcinogenesis.